The present invention relates to a rotary encoder used, for example, as a moving pitch sensor for detecting an angle of rotation of a rotating shaft.
Conventional rotary encoders of this type are of such a construction as shown in FIG. 6 in which a fixed split plate 3 as an arcuate plate having slits 3a formed at equal intervals, and a rotary slit plate 5 mounted on a rotor 4 and having a multitude of slits 5a formed radially at equal intervals in a peripheral edge portion of a disk, are disposed between a light emitting portion 1 constituted by a light emitting diode and a light sensing portion 2 constituted by a photo diode.
In the rotary encoders of such a construction, however, in order to make occurate the detection angle with regard to rotation of the rotor 4, namely, the movable slit plate 5, there is no method other than either forming the slits 3a and 5a finely in a high density or enlarging the diameters of the slit plates 3 and 5. But larger diameters of the slit plates 3 and 5 result in an increase in size of the apparatus, and an extremely difficult technique is involved in forming the slits 3a and 5a finely in a high density. Therefore therefore, rotary encoders of the above construction encounter a resolution limit.